The Sounders remained atop the league's Western Conference. The defending MLS Cup champions have won five of their past six matches and improved to 7-2-1 since returning from the MLS is Back Tournament.
RSL, which failed to put a shot on net and only scored on an own goal by Seattle's Nouhou Tolo, lost for the fourth time in its past six matches and fell out of the eighth and final playoff spot in the West, surpassed by Houston, which defeated FC Dallas 2-0.
It was the eighth goal of the season for Morris, matching the absent Raul Ruidiaz for the team lead. Morris has eight goals and seven assists this season, second in MLS in total points to Toronto's Alejandro Pozuelo, who has 16 (nine goals, seven assists).
Morris scored in the 28th minute, with assists going to Cristian Roldan and Lodeiro.
Lodeiro's pass sent Roldan alone down the right wing. The midfielder delivered a low cross into the penalty area that forward Will Bruin stepped over, allowing the ball to go to Morris at the top of the 6-yard box.
The cross was just a bit behind Morris, but he was able to reach his right foot back to chip the ball inside the near post as RSL goalkeeper Andrew Putna was leaning the other way.
Gomez Andrade scored on a header from the top of the 6-yard box in the 61st minute off a free kick from Lodeiro from about 30 yards out on the right wing.
Both teams were short-handed because of international duty. The Sounders were without forward Ruidiaz (Peru), midfielder Gustav Svensson (Sweden) and defender Xavier Arreaga (Ecuador), while RSL played without playmaking midfielder Albert Rusnak (Slovakia).